Power Semiconductor Devices Having Orthogonal Gate Electrodes and Ohmic Lines for Improved On-State Resistance Performance

The present invention relates to power semiconductor devices and, more particularly, to gate-controlled power semiconductor devices.

The Metal Oxide Semiconductor Field Effect Transistor (“MOSFET”) is a well-known type of semiconductor transistor that may be used as a switch. A MOSFET is a three terminal device that has gate, drain and source terminals and a semiconductor body. The semiconductor body is referred to herein as a “semiconductor layer structure” and may include one or more semiconductor layers/regions. A source region and a drain region that each have a first conductivity type are formed in the semiconductor layer structure and are separated from each other by a channel region that has a second conductivity type. A gate electrode is disposed adjacent the channel region and separated from the channel region by a thin oxide layer. A MOSFET may be turned on or off by setting a bias voltage that is applied to the gate electrode to be above or below a threshold value (which may be a negative voltage). When a MOSFET is turned on (i.e., it is in its “on-state”), current is conducted through the channel region between the source and drain regions. When the bias voltage is reduced below the threshold level, the current ceases to conduct through the channel region.

An n-type MOSFET has source and drain regions that have n-type (electron) conductivity and a channel region that has p-type (hole) conductivity (i.e., an “n-p-n” design). An n-type MOSFET turns on when the gate bias voltage that is applied to the gate electrode is sufficient to create a conductive n-type inversion layer in the p-type channel region, thereby electrically connecting the n-type source and drain regions and allowing for majority carrier conduction therebetween. A p-type MOSFET has a “p-n-p” design (i.e., p-type source and drain regions and an n-type channel region) and turns on when a gate bias voltage is applied to the gate electrode that is sufficient to create a conductive p-type inversion layer in the n-type channel region to electrically connect the p-type source and drain regions. Herein, the terms “first conductivity type” and “second conductivity type” are used to indicate either n-type or p-type conductivity, where the first and second conductivity types are different. Thus, if a first region of a device has a first conductivity type and a second region of the device has a second conductivity type, this means either that the first region has n-type conductivity and the second region has p-type conductivity or, alternatively, that first region has p-type conductivity and the second region has n-type conductivity.

Because the gate electrode of a MOSFET is insulated from the channel region by the gate oxide layer, minimal gate current is required to maintain the MOSFET in its on-state or to switch the MOSFET between its off-state and its on-state. The gate current is kept small during switching because the gate forms a capacitor with the channel region. Thus, only minimal charging and discharging current is required during switching, allowing for less complex gate drive circuitry and faster switching speeds. MOSFETs may be stand-alone devices or may be combined with other devices. For example, an Insulated Gate Bipolar Transistor (“IGBT”) is a semiconductor device that includes both a MOSFET and a Bipolar Junction Transistor (“BJT”) that combines the high impedance gate electrode of the MOSFET with the small on-state conduction losses that may be provided by a BJT.

In many applications, MOSFETs may need to carry large currents and/or be capable of blocking high voltages (e.g., hundreds or thousands of volts of electric potential). Such MOSFETs are often referred to as “power” MOSFETs. Power MOSFETs are often fabricated from wide band-gap semiconductor materials (herein, the term “wide band-gap semiconductor” encompasses any semiconductor having a band-gap of at least 1.4 eV). Power MOSFETs and other power semiconductor devices are often formed in silicon carbide (“SiC”), which has a number of advantageous characteristics including, for example, a high electric field breakdown strength, high thermal conductivity, high electron mobility, high melting point and high-saturated electron drift velocity.

MOSFETs can have a lateral structure or a vertical structure. In a device having a lateral structure, the drain, gate and source terminals are on the same major surface (i.e., top or bottom) of a semiconductor layer structure. In contrast, in a device having a vertical structure, at least one terminal is provided on each major surface of the semiconductor layer structure (e.g., the source and gate may be on the top surface of the semiconductor layer structure and the drain may be on the bottom surface of the semiconductor layer structure).

The semiconductor layer structure of a power semiconductor device includes an “active region” in which one or more functional semiconductor devices are formed. The active region acts as a main junction for blocking voltage during reverse bias (off-state) operation and for providing current flow during forward bias (on-state) operation. The power semiconductor device may also have an edge termination structure such as guard rings or a junction termination extension in a termination region of the semiconductor layer structure that is adjacent (and typically surrounding) the active region. The edge termination structure may, among other things, reduce electric field crowding effects that can occur at the outer edges of a power semiconductor device. Typically, multiple power semiconductor devices are formed in/on a common wafer, and each power semiconductor device will typically have its own edge termination structure. After the wafer is fully processed, the resultant structure may be diced to separate the individual edge-terminated power semiconductor devices. Each power semiconductor device may have a unit cell structure in which the active region of each power semiconductor device includes a plurality of individual “unit cell” devices that are electrically connected in parallel and that together function as a single power semiconductor device.

Vertical gate-controlled power semiconductor devices can have a planar gate electrode design in which the gate electrodes are formed on top of the semiconductor layer structure or, alternatively, may have the gate electrodes formed within gate trenches in the semiconductor layer structure, which are typically referred to as gate trench devices. With the planar gate electrode design, the channel region of each unit cell transistor is horizontally disposed underneath the gate electrode. In contrast, in gate trench devices, the channels are typically vertically disposed adjacent sidewalls of the gate electrodes.

One failure mechanism for a power MOSFET is the so-called “breakdown” of the gate oxide layer. The gate oxide layer is subjected to high electric fields during normal device operation. The high electric fields degrade the gate oxide layer over time, and may eventually result in failure of the device. When gate trench MOSFETs operate in reverse blocking operation (i.e., when the MOSFET is in its off-state), the source terminal of the MOSFET is typically grounded, the gate terminal is typically grounded or at a negative bias voltage, and the drain terminal is typically at a high positive voltage. During such reverse blocking operations, high electric fields extend upwardly from the drain terminal (which is on the lower surface of the semiconductor layer structure) toward the upper surface of the semiconductor layer structure. Thus, under reverse blocking operation, the portions of the gate oxide layers lining the bottoms of the gate trenches experience the highest electric field levels. The stress on the gate oxide layer caused by these electric fields generates defects in the oxide material, and these defects build up over time. When the concentration of defects reaches a critical value, a so-called “percolation path” may be created through the gate oxide layer that electrically connects the gate electrode to the source region, thereby creating a short-circuit that can destroy the device. The “lifetime” of a gate oxide layer (i.e., how long the device can be operated before breakdown occurs) is a function of, among other things, the magnitude of the electric field that the gate oxide layer is subjected to and the length of time for which the electric field is applied. Generally speaking, the relationship between the magnitude of the applied electric field and gate oxide lifetime may be generally linear when the gate oxide lifetime is plotted on a logarithmic scale, meaning that as the electric field level is increased, the lifetime of the gate oxide layer decreases exponentially.

Pursuant to some embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a drift region having a first conductivity type, a first gate electrode on the semiconductor layer structure that extends along a first longitudinal axis, a second gate electrode on the semiconductor layer structure that extends along a second longitudinal axis, and a first ohmic line that extends continuously in the semiconductor layer structure along a first transverse axis. The first and second longitudinal axes cross the first transverse axis when the semiconductor device is viewed from above.

In some embodiments, the first longitudinal axis extends in parallel to the second longitudinal axis. In some embodiments, the first transverse axis crosses the first longitudinal axis at an angle of 90°.

In some embodiments, the semiconductor device may further comprise a dielectric layer that extends continuously in a direction parallel to the first transverse axis to cover the first gate electrode and the second gate electrode and an upper surface of the semiconductor layer structure that is in between the first gate electrode and the second gate electrode.

In some embodiments, the first gate electrode is in a first gate trench in the semiconductor layer structure and the second gate electrode is in a second gate trench in the semiconductor layer structure. In some embodiments, the first gate trench and the second gate trench each have a respective first end that is adjacent the first ohmic line. In some embodiments, the semiconductor device may further comprise a third gate electrode that extends along a third longitudinal axis in a third gate trench in the semiconductor layer structure and a fourth gate electrode that extends along a fourth longitudinal axis in a fourth gate trench in the semiconductor layer structure, where the first longitudinal axis is colinear with the third longitudinal axis and the second longitudinal axis is colinear with the fourth longitudinal axis. In some embodiments, the first ohmic line is in between the first gate trench and the third gate trench and is in between the second gate trench and the fourth gate trench when the semiconductor device is viewed from above.

In some embodiments, the semiconductor device may further comprise a second ohmic line that extends continuously in the semiconductor layer structure along a second transverse axis, wherein the first and second longitudinal axes cross the second transverse axis when the semiconductor device is viewed from above. In such embodiments, the first transverse axis may extend in parallel to the second transverse axis. In some embodiments, the first gate electrode and the second gate electrode may be positioned between the first ohmic line and the second ohmic line when the semiconductor device is viewed from above.

In some embodiments, a first portion of the semiconductor layer structure that is in between the first gate trench and the second gate trench comprises a drift region having a first conductivity type, a source region having the first conductivity type and a well region having a second conductivity that is in between the drift region and the source region. In such embodiments, the first longitudinal axis may extend in a first direction, and the semiconductor device may also be configured so that during on-state operation a source-drain current flows in the first direction through the source region in the first portion of the semiconductor layer structure.

In some embodiments, the semiconductor device may further comprise a silicide layer on the source region and a dielectric layer on the silicide layer, where the silicide layer directly contacts both the source region and the dielectric layer. In such embodiments, the silicide layer may extend continuously on an upper surface of the source region from a first sidewall of the first gate trench to a first sidewall of the second gate trench.

In some embodiments, the semiconductor device may further comprise a supplemental gate electrode that extends in a first supplemental gate trench in the semiconductor layer structure, the supplemental gate electrode having a longitudinal axis that is perpendicular to the first and second longitudinal axes. In such embodiments, a first end of the first gate electrode contacts the supplemental gate electrode and a first end of the second gate electrode contacts the supplemental gate electrode. In these embodiments, the supplemental gate electrode may extend along a second transverse axis that is parallel to the first transverse axis. In some embodiments, the semiconductor layer structure may comprise a drift region having a first conductivity type, a source region having the first conductivity type, a well region having a second conductivity that is in between the drift region and the source region, and a trench shield having the second conductivity type that extends underneath the first gate trench, the second gate trench and the supplemental gate trench. In such embodiments, the semiconductor layer structure may further comprise a trench shield connection pattern having the second conductivity type that extends along a sidewall of the supplemental gate trench.

In some embodiments, a width of a portion of the semiconductor layer structure that is in between the first gate trench and the second gate trench is less than a width of the first gate trench.

Pursuant to some embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a drift region having a first conductivity type, a source region having the first conductivity type and a well region having a second conductivity type between the drift region and the source region. These semiconductor devices further comprise a first gate electrode on the semiconductor layer structure that has a first longitudinal axis that extends in a first direction, a second gate electrode on the semiconductor layer structure that has a second longitudinal axis that extends in the first direction, and a dielectric layer that extends continuously on the semiconductor layer structure in a second direction, where the dielectric layer crosses the first gate electrode, the second gate electrode and a first portion of the source region that is in between the first gate electrode and the second gate electrode.

In some embodiments, the second direction is perpendicular to first direction.

In some embodiments, the dielectric layer directly contacts the first portions of the source region.

In some embodiments, the semiconductor device may further comprise a silicide layer on the first portions of the source region, and the dielectric layer directly contacts the silicide layer.

In some embodiments, the semiconductor device may further comprise a source metallization, wherein the semiconductor layer structure further comprises a first ohmic line that extends in a second direction that is perpendicular to the first direction, wherein the source metallization directly contacts the first ohmic line. In some embodiments, the semiconductor layer structure may also include a second ohmic line that extends in the second direction, and the dielectric layer may cover portions of the semiconductor layer structure that are in between the first ohmic line and the second ohmic line. In some embodiments, the first gate electrode and the second gate electrode may be positioned between the first ohmic line and the second ohmic line when the semiconductor device is viewed from above.

In some embodiments, the first gate electrode is in a first gate trench in the semiconductor layer structure and the second gate electrode is in a second gate trench in the semiconductor layer structure, the semiconductor device further comprising a third gate electrode that is in a third gate trench in the semiconductor layer structure, and a fourth gate electrode that is in a fourth gate trench in the semiconductor layer structure. In such embodiments, the first gate trench and the second gate trench each have a respective first end that is adjacent the first ohmic line. In some embodiments, a longitudinal axis of the first gate trench is colinear with a longitudinal axis of the third gate trench, and a longitudinal axis of the second gate trench is colinear with a longitudinal axis of the fourth gate trench. In some embodiments, the first ohmic line is in between the first gate trench and the third gate trench and the first ohmic line is also in between the second gate trench and the fourth gate trench.

In some embodiments, a width of a portion of the semiconductor layer structure that is in between the first gate trench and the second gate trench is less than a width of the first gate trench.

In some embodiments, the first gate trench has a first longitudinal axis that extends in a first direction, and the semiconductor device is configured so that during on-state operation a source-drain current flows in the first direction through the source region in a first portion of the semiconductor layer structure that is in between the first gate trench and the second gate trench.

In some embodiments, the semiconductor device may further comprise a supplemental gate electrode that extends in a first supplemental gate trench in the semiconductor layer structure, the supplemental gate electrode having a longitudinal axis that is perpendicular to a first longitudinal axis of the first gate trench. In such embodiments, a first end of the first gate electrode contacts the supplemental gate electrode.

Pursuant to some embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a source region having the first conductivity type, a silicide layer on the source region, and a dielectric layer on the silicide layer so that the silicide layer directly contacts both the source region and the dielectric layer.

In some embodiments, the semiconductor device may further comprise a first gate electrode that has a first longitudinal axis that extends in a first direction and a second gate electrode that has a second longitudinal axis that extends in the first direction.

In some embodiments, the semiconductor device may further comprise a first ohmic line that extends continuously in the semiconductor layer structure along a first transverse axis and a second ohmic line that extends continuously in the semiconductor layer structure along a second transverse axis, where the first longitudinal axis extends perpendicular to both the first transverse axis and the second transverse axis when the semiconductor device is viewed from above. In some embodiments, the first silicide layer covers an entirety of an upper surface of a first portion of the source region that is in between the first gate electrode, the second gate electrode, the first ohmic line and the second ohmic line.

In some embodiments, the first gate electrode is in a first gate trench in the semiconductor layer structure and the second gate electrode is in a second gate trench in the semiconductor layer structure. In some embodiments, a width of a portion of the semiconductor layer structure that is in between the first gate trench and the second gate trench is less than a width of the first gate trench.

Pursuant to still further embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a drift region having a first conductivity type, a source region having the first conductivity type and a well region having a second conductivity type between the drift region and the source region, a first gate electrode on the semiconductor layer structure that has a first longitudinal axis that extends in a first direction, a second gate electrode on the semiconductor layer structure that has a second longitudinal axis that extends in the first direction, the second gate electrode adjacent the first gate electrode in a second direction that is perpendicular to the first direction, and a source metallization on an upper surface of the semiconductor layer structure, where the source metallization has a plurality of downwardly-extending protrusions that directly contact an upper surface of the semiconductor layer structure, where the downwardly-extending protrusions have respective longitudinal axes that extend in the second direction.

In some embodiments, a dielectric layer completely covers a portion of the upper surface of the semiconductor layer structure that is in between the first gate electrode and the second gate electrode.

In some embodiments, a first gate electrode and the second gate electrode are in between first and second of the downwardly-extending protrusions when the semiconductor device is viewed from above.

In some embodiments, the first gate electrode is in a first gate trench in the semiconductor layer structure and the second gate electrode is in a second gate trench in the semiconductor layer structure. In some embodiments, the semiconductor device may further comprise a third gate electrode that extends along a third longitudinal axis in a third gate trench in the semiconductor layer structure and a fourth gate electrode that extends along a fourth longitudinal axis in a fourth gate trench in the semiconductor layer structure, where the first longitudinal axis is colinear with the third longitudinal axis and the second longitudinal axis is colinear with the fourth longitudinal axis. In some embodiments, a first of the downwardly-extending protrusions is in between the first gate trench and the third gate trench and is in between the second gate trench and the fourth gate trench when the semiconductor device is viewed from above. In some embodiments, the semiconductor device may further comprise a first ohmic line in the semiconductor layer structure, wherein the first of the downwardly-extending protrusions directly contacts the first ohmic line.

Pursuant to some embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a drift region having a first conductivity type, a source region having the first conductivity type and a well region having a second conductivity type between the drift region and the source region. These semiconductor devices further comprise a first gate trench on the semiconductor layer structure that has a first longitudinal axis that extends in a first direction, a second gate trench on the semiconductor layer structure that has a second longitudinal axis that extends in the first direction, the second gate trench adjacent the first gate trench, and a first ohmic line in the semiconductor layer structure that has a third longitudinal axis that extends in a second direction, and a second ohmic line in the semiconductor layer structure that has a fourth longitudinal axis that extends in the second direction. A portion of the source region that is within a first region that is in between the first gate trench, the second gate trench, the first ohmic line and the second ohmic line when the semiconductor device is viewed in plan view completely covers a portion of the well region that is within the first region.

In some embodiments, the semiconductor device may further comprise a silicide layer on an upper surface of the source region in the first region.

In some embodiments, the semiconductor device may further comprise a dielectric layer that completely covers an upper surface of the source region in the first region.

In some embodiments, the semiconductor device may further comprise a third gate electrode that extends along a third longitudinal axis in a third gate trench in the semiconductor layer structure and a fourth gate electrode that extends along a fourth longitudinal axis in a fourth gate trench in the semiconductor layer structure, where the first longitudinal axis is colinear with the third longitudinal axis and the second longitudinal axis is colinear with the fourth longitudinal axis. In some embodiments, the first ohmic line is in between the first gate trench and the third gate trench and is in between the second gate trench and the fourth gate trench when the semiconductor device is viewed from above.

In some embodiments, a width of a portion of the semiconductor layer structure that is in between the first gate trench and the second gate trench is less than a width of the first gate trench.

Pursuant to some embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a drift region having a first conductivity type, a source region having the first conductivity type and a well region having a second conductivity type between the drift region and the source region, a first gate electrode in the semiconductor layer structure, the first gate electrode having a first longitudinal axis that extends in a first direction, and a second gate electrode in the semiconductor layer structure, the second gate electrode having a second longitudinal axis that extends in the first direction, the second gate electrode adjacent the first gate electrode. The semiconductor device is configured so that during on-state operation a source-drain current flows in the first direction through a first portion of the source region that is in between the first gate electrode and the second gate electrode.

In some embodiments, the semiconductor device may further comprise a silicide layer on the first portion of the source region and a dielectric layer on the silicide layer, where the silicide layer directly contacts both the first portion of the source region and the dielectric layer.

Pursuant to some embodiments of the present invention, semiconductor device are provided that comprise a semiconductor layer structure comprising a drift region having a first conductivity type, a first gate electrode on the semiconductor layer structure that extends along a first longitudinal axis, a second gate electrode on the semiconductor layer structure that extends along a second longitudinal axis, a first ohmic line that extends continuously in the semiconductor layer structure along a first transverse axis, a second ohmic line that extends continuously in the semiconductor layer structure along a second transverse axis that is parallel to the first transverse axis, and a dielectric layer that completely covers an upper surface of a first region of the semiconductor layer structure that is in between the first and second gate electrodes and the first and second ohmic lines.

In some embodiments, an entirety of the upper surface of the first region of the semiconductor layer structure is a source region that has the first conductivity type.

In some embodiments, the first longitudinal axis crosses the first transverse axis at an angle of 90° when the semiconductor device is viewed from above.

In some embodiments, the semiconductor device may further comprise a source metallization that directly contacts the entirety of first region of the semiconductor layer structure. In some embodiments, the source metallization also directly contacts the first ohmic line and the second ohmic line.

Two-part reference numerals that include two numbers separated by a dash (-) are sometimes used in the figures and the discussion that follows to identify instances of multiple like elements. The full reference number may be used to refer to individual instances of the like element while the first part of the reference number may be used to refer to the like elements collectively.

It will be appreciated that the sizes (e.g., the thicknesses) of various regions in the drawings are not drawn to scale to allow enlargement of other regions of the drawings. For example, the substrates and drift regions of the power semiconductor devices shown in the drawings are depicted as being much thinner in the figures than they are in practice so that details of thinner upper layers and regions of the semiconductor devices can be more clearly depicted.

The “pitch” of a semiconductor device having a unit cell structure refers to the center-to-center distance between adjacent unit cells. As the pitch is decreased (meaning the unit cells are packed closer together), the integration level of a semiconductor device increases, which is desirable. For gate-controlled semiconductor devices, the pitch may be defined as the center-to-center distance between adjacent gate electrodes. Vertical gate-controlled power semiconductor devices such as power MOSFETs and IGBTs that have a gate trench design have a smaller pitch than comparable planar gate-controlled vertical power semiconductor devices. The increased degree of integration provided by the reduced pitch lowers the on-state resistance per unit area. Moreover, vertical power semiconductor devices that have a gate trench design exhibit increased carrier mobility (2-4 times higher) than comparable planar gate vertical power semiconductor devices, which acts to further reduce the on-state resistance. However, as discussed above, gate trench power MOSFETs are susceptible to oxide reliability issues due to the presence of high electric fields in the gate oxide layers. Due to electric field crowding effects, the electric field levels in the lower “corners” of the gate oxide layer at the bottom edges of the gate trench may be particularly high (i.e., the portions of the gate oxide layers that cover the region where the sidewalls of the gate trenches merge into the bottoms of the respective gate trenches). Moreover, due to the difference in permittivity between silicon carbide and silicon oxide, the electric field in a silicon oxide gate oxide layer may be about 2.6 times higher than the electric field in the silicon carbide semiconductor layer structure adjacent the gate oxide layer.

So-called “trench shielding regions” (also called “bottom shields” or “trench shields”) are often provided underneath the gate trenches of gate trench power MOSFETs in order to reduce the electric field levels in the bottom portion of the gate oxide layer during reverse blocking operation. These trench shielding regions are formed by doping the portions of the semiconductor layer structure underneath the gate trenches with dopants having the same conductivity type as the dopants included in the channel regions of the device. The trench shielding regions are typically formed via one or more ion implantation processes in which p-type dopant ions (for an n-type MOSFET) are implanted through the bottom surfaces of the gate trenches. The trench shielding regions are electrically connected to the source terminal of the MOSFET by p-type trench shield connection patterns. While trench shielding regions can significantly reduce the electric field levels in the gate oxide layers, they also act to funnel the on-state currents through smaller regions (as the on-state currents flow around the p-type regions), thereby increasing the on-state resistance. Thus, there is an inherent trade-off between on-state resistance performance and device reliability in vertical gate trench power semiconductor devices.

1 FIG.A 1 FIG.A 1 FIG.B 1 FIG.A 1 1 is a schematic plan view of a small portion of a conventional gate trench power MOSFET that includes trench shielding regions. In, the upper metallization and dielectric layers are omitted to show the upper surface of the semiconductor layer structure and the gate electrodes.is a cross-sectional view taken along lineB-B ofwith the upper metallization and dielectric layers added to provide context.

1 FIG.A 1 FIG.A 1 FIG.A 1 FIG.A 2 2 FIGS.A-B 1 60 60 60 1 80 60 80 1 80 80 40 34 60 80 40 34 80 40 34 80 34 40 + Referring first to, power MOSFETincludes a wide bandgap semiconductor layer structurethat comprises a plurality of silicon carbide layers. The semiconductor layer structurehas first and second major surfaces that extend in the x-direction and the y-direction of an x-y-z coordinate system. The semiconductor layer structurehas a thickness in the z-direction, which is also referred to herein as the depth direction. The MOSFETincludes a large number of gate trenchesthat are formed in the upper portion of the semiconductor layer structure. Only two gate trenchesare shown in, asonly illustrates a small representative section of power MOSFET. Each gate trenchhas a longitudinal axis that extends in the x-direction so that the gate trenchesextend in parallel to each other. A pair of heavily-doped (n) n-type silicon carbide source regionsand a heavily-doped p-type well contact regionare formed in the upper surface of the semiconductor layer structurebetween each pair of adjacent gate trenches. While in, two source regionsand a single well contact regionare provided between each pair of adjacent gate trenches, it will be appreciated that other arrangements are possible. For example, in the device of(discussed below), a single source regionand a plurality of well contact regionsthat are spaced-apart from each other in the x-direction provided between each pair of adjacent gate trenches, with the well contact regionsformed as islands within the single source region.

1 FIG.B 60 10 20 10 20 20 22 20 22 30 22 34 40 30 80 60 20 50 80 80 70 80 82 80 70 72 82 90 72 40 34 6 10 − Referring to, the semiconductor layer structureincludes a thick heavily-doped n-type silicon carbide semiconductor substrate. A lightly-doped n-type (n) silicon carbide drift region(also referred to as a “drift layer”) is provided on the upper surface of the substrate. An upper portion of the drift regionmay be more heavily doped than the remainder of the drift region, and this more highly-doped portionof the drift regionis referred to herein as a JFET region(which may be a continuous region or a plurality of discontinuous regions, as shown). A plurality of moderately-doped p-type wells(also referred to as “p-wells”) are formed on the JFET region, typically by ion implantation. The well contact regionsand the source regionsare formed on upper portions of the p-wells, typically by ion implantation. The gate trenchesextend downwardly through upper portions of the semiconductor layer structureinto the drift region. Moderately-doped p-type trench shielding regionsare formed below each gate trench, and may extend underneath the respective gate trenches. A gate oxide layeris formed conformally within each gate trench, and gate electrodesare formed in the respective gate trencheson the gate oxide layers. An intermetal dielectric patterncovers the gate electrodes. A source metallizationis formed on the intermetal dielectric patternand on the n-type source regionsand the p-type well contact regions. A metal drain contactis formed on the lower surface of the substrate.

24 60 80 50 24 2 2 FIGS.A-B A so-called “JFET gapis defined in the semiconductor layer structurebetween each pair of adjacent gate trenches. As used herein, the “JFET gap” refers to the distance in the y-direction (i.e., a direction perpendicular to the longitudinal axes of the gate trenches and also perpendicular to the depth direction) between p-type shielding regions in the semiconductor layer structure such as the trench shielding regionsand support shields (see). The on-state current flows through the JFET gapsas the on-state current does not flow in the p-type shielding regions.

90 40 34 40 34 92 92 92 34 40 92 92 1 ohmic ohmic ohmic The source metallizationis typically designed to form an ohmic contact to both the n-type source regionsand the p-type well contact regions. Thus, the longitudinally-extending combination of the source region(s)and the well contact region(s)that are provided between a pair of adjacent gate trenches are sometimes referred to as an “ohmic line”. The width Wof each ohmic line(i.e., the extent of the ohmic linein the y-direction) is related to the contact resistance and is selected based on the resistivities of the well contact regionsand the source regions. Photolithographic process limitations may also limit how small the width Wof the ohmic linemay be made. Thus, the requirements for the width Wof the ohmic linemay limit the cell pitch of the power MOSFET.

ohmic ohmic ohmic 92 24 92 24 1 80 50 60 30 92 1 The width Wof the ohmic linemay be, for example, between 1.0-2.0 microns. The width of the JFET gapthat would optimize device performance, however, may be less the width Wof the ohmic line, but the contact resistance requirements and/or processing limitations may necessitate a larger JFET gapthan is optimal, resulting in an increased cell pitch. The expanded cell pitch increases the on-state resistance, and also negatively affects the reverse blocking capabilities of power MOSFETdue to the increased separation between adjacent gate trenches, since the increased distance between adjacent trench shielding regionsallows high electric fields to extend farther upwardly into the semiconductor layer structureduring reverse blocking operation. These higher electric field levels may deplete the well regions, allowing for punch through. Thus, the required width Wof the ohmic linesmay reduce device integration and also reduce the maximum blocking voltage of power MOSFET.

2 FIG.A 2 FIG.A 2 FIG.B 2 FIG.A 1 2 2 In order to increase the supportable reverse blocking voltage, many power MOSFET designs include so-called support shields that are provided in the JFET gaps between adjacent gate trenches.is a schematic plan view of a small portion of a conventional gate trench power MOSFET′ that includes support shields. The upper metallization and dielectric layers are omitted in.is a cross-sectional view taken along lineB-B ofwith the upper metallization and dielectric layers included.

1 1 2 2 FIGS.A-B toA-B 1 1 FIGS.A-B 1 1 1 52 34 24 52 60 70 1 52 1 52 52 1 As can be seen by comparing, power MOSFET′ is very similar to power MOSFET, except that power MOSFET′ includes moderately-doped p-type support shieldsthat extend downwardly from the well contact regionsin the middle of the JFET gaps. The p-type support shieldsact to suppress the electric fields in the upper portion of the semiconductor layer structureduring reverse blocking operation, thereby lowering the electric fields in the gate oxide layers, which improves the reliability of power MOSFET′. Unfortunately, however, the addition of the support shieldsincreases the “pitch” of power MOSFET′ (i.e., the distance between adjacent unit cells in the y-direction), since the pitch must be increased to make room for the support shields. Thus, the provision of support shieldsmay be an imperfect solution to the above-discussed problems with MOSFETof.

ohmic Pursuant to embodiments of the present invention, power MOSFETs and other gate-controlled semiconductor devices are provided that may have improved trade-offs between on-state resistance performance and device reliability, and which may also exhibit improved short circuit switching behavior. The power semiconductor devices according to embodiments of the present invention may have ohmic lines that cross the gate electrodes (e.g., extend perpendicularly to the gate electrodes) as opposed to ohmic lines that extend in parallel to the gate electrodes. Since the ohmic lines do not extend in the x-direction in between the gate electrodes, since the contact resistance is no longer a function of the width W. Consequently, the cell pitch may be decreased (meaning the distance between adjacent gate electrodes is reduced). Since an aggressive cell pitch may be used, the need for support shields may be eliminated as the JFET gaps are already small. The reduced cell pitch lowers the on-resistance per unit area since the number of unit cells is increased, and the small JFET gaps provide good shielding for the gate oxide layers and protect against punch-through the p-wells during reverse blocking operation. The JFET gaps in power semiconductor devices according to embodiments of the present invention may, for example, be between 0.5-1.6 microns depending on the dose and implant energy of the ion implantation step used to form the trench shields.

Since the ohmic lines may extend perpendicularly to the gate trenches (meaning that a longitudinal axis of each ohmic line may cross longitudinal axes of the gate trench at angles of 90°), the portions of the upper surface of the semiconductor layer structure that are between the gate trenches may be covered with a dielectric layer, even though such portions of the semiconductor layer structure are part of the active region of the device. During on-state operation, current may flow vertically (i.e., in the depth direction) from the source metallization into the ohmic lines, and may then flow generally horizontally into the source regions between adjacent gate trenches as well as flowing vertically through the source regions and the channel regions in the p-wells into the drift region of the device. Notably, this design increases the average length of the overall on-state current path. Increasing the on-state current path is non-intuitive, as longer current paths generally have higher resistance. Here, however, the current path is increased by routing the current to flow horizontally through the n-type source region, which is a highly-doped region that has a relatively low resistance. As such, the increase in the resistance caused by the increased current path may be less than the reduction in the resistance provided by the increased integration gained by the aggressive cell pitch. Moreover, in some embodiments, a silicide layer may be formed at the upper surface of the portions of the source regions that are in between adjacent gate trenches. Since a silicide layer may have a resistance that is orders of magnitude less than the resistance of the source region, much of the horizontally-flowing on-state current will flow through the silicide regions, and thus the impact of the horizontally-flowing on-state current on the on-state resistance may be negligible.

In some embodiments, the ohmic lines may be continuous ohmic lines and the gate trenches may be discontinuous gate trenches (since the ohmic lines interrupt the gate trenches). Such a design may be preferred in some cases as a continuous ohmic line has more surface area for the ohmic contact (and hence the width of the ohmic line may be reduced). An important parameter in the power semiconductor devices according to embodiments of the present invention is the separation between adjacent ohmic lines, as this will define the source resistance of the device. The source resistance can therefore readily be tuned by adjusting the pitch of the ohmic lines, and the devices can be designed to have a higher source resistance than is exhibited by conventional power semiconductor devices. The increased source resistance may improve the short circuit capabilities of the device, as will be explained in greater detail herein.

3 12 FIGS.A-C Embodiments of the present invention will now be described in more detail with reference to. It will be appreciated that features of the different embodiments disclosed herein may be combined in any way to provide many additional embodiments. Thus, it will be appreciated that various features of the present invention are described below with respect to specific examples, but that these features may be added to other embodiments and/or used in place of example features of other embodiments to provide many additional embodiments. Thus, the present invention should be understood to encompass these different combinations. Additionally, while the example embodiments focus on MOSFET implementations, it will be appreciated that the same techniques may be used in other gate trench power semiconductor devices such as insulated gate bipolar transistors (IGBTs), gate controlled thyristors and the like. It will also be appreciated that the term MOSFET is used broadly to encompass devices that use both oxide-based gate dielectric layers and non-oxide gate dielectric layers (e.g., nitrides, high dielectric constant materials, etc.), and that the gate electrodes of the MOSFETs may comprise any conductive material (including semiconductor materials) and is not limited to metal gate electrodes.

3 FIG.A 3 FIG.B 100 100 100 160 160 160 160 is a schematic top view of a gate trench silicon carbide power MOSFETaccording to certain embodiments of the present invention.is a schematic plan view of the power MOSFETwith an upper protective layer omitted to show the full gate and source metallization. As will be discussed below, power MOSFETincludes a semiconductor layer structurethat comprises a plurality of semiconductor layers/regions. At least one of the semiconductor layers in the semiconductor layer structuremay be a silicon carbide layer. Various metal and/or dielectric layers are formed on either side of the semiconductor layer structureand/or formed in trenches in the semiconductor layer structure.

3 FIG.A 4 4 FIGS.A-D 4 4 4 FIGS.A andC-D 100 102 104 1 104 2 160 160 106 160 102 104 106 100 102 104 106 109 100 102 104 Referring to, power MOSFETincludes a gate padand one or more source pads-,-that are each formed on the upper side of the semiconductor layer structure(the semiconductor layer structureis shown in). A metal drain pad(see) is provided on the bottom side of the semiconductor layer structure. The gate pad, the source padsand the drain padform the respective gate, source and drain terminals of power MOSFET. The gate and source pads,may each be formed of a metal, such as aluminum, that bond wires can be readily attached to via conventional techniques such as thermo-compression or soldering. The drain padmay likewise be a metal pad. A protective layersuch as a polyimide layer may cover the entire upper surface of power MOSFETexcept for the gate and source pads,.

3 FIG.A 3 FIG.A 100 190 160 104 1 104 2 190 160 104 109 190 190 107 100 108 100 107 108 100 102 Still referring to, the power MOSFETincludes a source metallization(indicated by the dashed boxes in) that electrically connects certain regions of the semiconductor layer structureto the source pads-,-. The source metallizationmay include, for example, an ohmic contact layer (e.g., a metal silicide layer) that directly contacts the semiconductor layer structure, one or more optional adhesion and or barrier metal layers, and a bulk metal layer. Typically, the source padsare a part of the bulk metal layer that is exposed through the protective layer. Herein, the source metallizationwill be illustrated as a single layer for simplicity, but it will be appreciated that it typically includes multiple layers and may have any appropriate form. The source metallizationmay generally overlie or correspond to an “active region”of the power MOSFETwhere the unit cell transistors are located. An inactive regionof power MOSFETsurrounds the active region. The inactive regionmay include a termination region that extends around the periphery of the MOSFETthat includes guard rings, junction termination elements or other termination structures (not shown), a gate pad region that underlies the gate pad, and gate bus regions.

101 102 104 106 100 3 FIG.A Bond wiresare shown inthat may be used to connect the gate padand the source padsto external circuits or the like. The drain padon the bottom side of power MOSFETmay be connected to an external circuit through, for example, an underlying submount (not shown).

3 FIG.B 3 FIG.B 100 109 190 107 102 103 190 102 103 102 103 105 103 107 103 102 182 107 is another plan view of power MOSFETwith the polymide layeromitted to expose the full source and gate metallization. As shown in, the source metallizationextends throughout the active regionof the device. The gate metallization includes the gate padand a gate bus. The source metallizationis spaced apart from both the gate padand the gate busso that a single metal layer may be used to form the source metallization and the gate metallization. The gate padis spaced apart from the gate busso that the gate current may pass through one or more lumped gate resistors (not visible in the figures) that are formed underneath an intermetal dielectric layer. The lumped gate resistors may, for example, improve the electromagnetic interference (“EMI”) performance of the device and/or improve the stability of long feedback loops that are created as the lengths of the gate electrodes are increased in order to increase the power handling capability of the device. The metal gate busesextend around much of the periphery of the active region. The gate busesmay provide a low resistance path for distributing gate signals that are applied to the gate padto the gate electrodes(discussed below) that extend throughout the active region.

4 4 FIGS.A-D 3 3 FIGS.A-B 4 4 FIGS.A-D 3 FIG.A 4 FIG.A 4 FIG.B 4 4 FIGS.C andD 4 FIG.B 4 FIG.B 4 4 FIGS.C-D 100 100 4 4 4 4 illustrate a small portion of power MOSFET. The small portion of power MOSFETillustrated incorresponds to the region labeled A in.is a schematic perspective view of the region A, whileis a schematic top view of the portion A with the upper dielectric layers and the source metallization omitted to show the gate electrodes and the upper surface of the semiconductor layer structure.are cross-sectional views taken along linesC-C andD-D, respectively, ofwith the upper dielectric layers and the source metallization that are omitted inadded for context in.

4 4 FIGS.A-B 100 110 110 110 110 110 18 3 21 3 Referring to, power MOSFETincludes an n-type silicon carbide semiconductor substrate. The substratemay comprise, for example, a single crystal 4H silicon carbide semiconductor substrate that is heavily-doped with n-type impurities (i.e., an n+ silicon carbide substrate). The impurities may comprise, for example, nitrogen or phosphorous. In example embodiments, the n-type substratemay have a doping concentration of, for example, between 1×10atoms/cmand 1×10atoms/cm, although other doping concentrations may be used. The substratemay be relatively thick in some embodiments (e.g., 20-100 microns or more). The substratemay be partially or fully removed in some embodiments.

120 110 120 120 120 110 120 120 110 122 120 122 120 122 120 122 120 120 122 122 122 14 17 3 16 3 17 3 A lightly-doped n-type (n−) silicon carbide drift layeris provided on an upper surface of the substrate. The drift layermay also be referred to herein as a drift region. Typically, the drift layeris formed via an epitaxial growth process on the silicon carbide substrateand is doped during growth. The n-type drift regionmay have, for example, a doping concentration of 1×10to 5×10dopants/cm, with the doping level typically selected based on a blocking voltage rating of the device. The n-type drift regionmay be a thick region, having a vertical height above the substrateof, for example, 3-50 microns. A more heavily doped JFET regionis formed in the upper portion of the drift region. The JFET regionhas a higher peak doping concentration than the remainder of the drift region. In example embodiments, the JFET regionmay have a peak doping concentration that is between twice and ten times the peak doping concentration of the lower portion of the drift layer. The JFET regionis considered to be part of the drift layer, and has a higher doping concentration than the remainder of the drift region. The JFET regionmay be a continuous region or a plurality of discontinuous regions, and may have a relatively constant doping concentration or a graded doping concentration. In example embodiments, the peak doping concentration of the JFET regionmay be between 1×10dopants/cmand 5×10dopants/cm. The JFET regionmay have a thickness (i.e., extent in the depth direction) of, for example, between 0.3 and 1.0 microns.

130 130 120 130 130 130 16 3 19 3 A plurality of moderately-doped (p) p-type silicon carbide well regions(which may also be referred to herein as a “p-wells”) are formed on the upper surface of the n-type drift region. The p-wellsmay be formed, for example, via an ion implantation process. The p-wellsmay, for example, have a peak doping concentration of between 6×10dopants/cmand 1×10dopants/cm. The p-wellsmay have a thickness (i.e., extent in the depth direction) of, for example, between 0.3 and 0.6 microns.

140 130 140 160 140 140 20 3 Heavily-doped n-type (n+) silicon carbide source regionsare formed on or in upper portions of the respective p-wells. Each source regionmay extend, for example, to a maximum depth of between 0.2 microns and 1.0 microns from the upper surface of the semiconductor layer structure. The source regionsmay, for example, have a peak doping concentration that exceeds 1×10dopants/cm. The heavily-doped n-type silicon carbide source regionsmay be formed by ion implantation.

110 120 122 130 140 160 100 160 134 150 154 120 110 100 106 110 120 The substrate, the drift region(including the JFET region), the p-wellsand the source regionsare all silicon carbide regions and are all part of the semiconductor layer structureof power MOSFET. The semiconductor layer structurefurther includes several additional silicon carbide regions, discussed below, including p-type well contact regions, p-type trench shielding regionsand p-type trench shield connection patterns. The drift layerand the substratetogether act as a common drain region for the power MOSFET. The drain padis formed on the substrateopposite the drift region.

180 160 180 180 180 160 180 4 FIG.A A plurality of gate trenchesare formed in the upper portion of the semiconductor layer structure. Three gate trenchesare visible in. A longitudinal axis of each gate trenchextends in the x-direction. Each gate trenchmay, for example, extend to a maximum depth of between 0.5 microns and 1.5 microns from the upper surface of the semiconductor layer structure. The gate trenchesmay be formed via an etching process.

170 180 180 170 170 180 2 A gate oxide layeris provided in each gate trenchto cover the sidewalls and bottom surface of the gate trench. Each gate oxide layermay comprise, for example, a silicon oxide (SiO) pattern. The gate oxide layersmay be formed generally conformally within the respective gate trenches.

182 180 170 182 182 170 182 160 182 160 182 103 182 182 160 182 160 170 160 182 160 182 102 103 3 FIG.B A gate electrodeis formed in each gate trenchon the gate oxide layer. The gate electrodesmay comprise a conductive material such as a silicide (e.g., NiSi, TiSi, WSi, CoSi), a metal (e.g., Ti, Ta or W), a metal nitride (e.g., TiN, TaN or WN) or a doped semiconductor material (e.g., doped polycrystalline silicon). Most silicon carbide based power MOSFETs have doped polysilicon gate electrodes. The gate oxide layersmay insulate the gate electrodesfrom the semiconductor layer structure, thereby preventing the gate electrodesfrom short circuiting to the semiconductor layer structure. Each gate electrodemay connect to one of the gate buses(see). In the depicted embodiment, the gate electrodesare recessed so that the upper surface of each gate electrodeis below an upper surface of the semiconductor layer structure. It will be appreciated that in other embodiments the gate electrodesmay extend above and onto the upper surface of the semiconductor layer structure, with the gate oxide layeralso extending onto the upper surface of the semiconductor layer structureto insulate the gate electrodesfrom the upper surface of the semiconductor layer structure. The gate electrodesmay be connected to the gate padthrough the gate buses.

172 182 172 190 182 172 140 140 180 Intermetal dielectric layersare formed that cover each gate electrode. The intermetal dielectric layersinsulate the source metallizationfrom the gate electrodes. As will be discussed in further detail below, the intermetal dielectric layersmay also extend onto first portionsA of the source regionthat are in between pairs of adjacent gate trenches.

150 180 150 180 150 150 180 150 124 124 124 124 124 150 17 3 19 3 Moderately doped p-type trench shielding regionsare formed underneath each gate trench. Each trench shielding regionmay extend the full length of each gate trench. In example embodiments, the p-type trench shielding regionsmay have doping concentrations of between 1×10dopants/cmand 1×10dopants/cm. The trench shielding regionsmay, for example, be formed by ion implantation (typically into the bottoms of the gate trenches). The trench shielding regionsdefine JFET gaps. The width of the JFET gapsmay be set based on minimum gap required by the processing equipment and/or to optimize the on-state resistance based on the tradeoff between the resistance in the JFET gap region (which resistance increases as the JFET gapis narrowed due to current crowding) and the number of unit cells per unit area (which number increases as the JFET gapis reduced, and the larger number of unit cells acts to reduce the on-state resistance per unit area). In example embodiments, the width of the JFET gapmay be between 0.5-1.6 microns depending on the dose and implant energy of the ion implantation step used to form the trench shielding regions.

4 FIG.B 4 FIG.B 4 FIG.B 140 180 182 140 180 140 100 180 182 180 181 2 180 180 181 1 181 3 Referring to, it can be seen that the source regionsextend as continuous stripes in the x-direction. A plurality of gate trencheswith the gate electrodestherein extend in between each pair of adjacent source regionstripes. The gate trenchesthat extend between a pair of adjacent source regionstripes may be aligned in the x-direction. As such, when viewed from above, power MOSFEThas gate trenches(with gate electrodestherein) that are arranged in rows and columns. In the view of, the gate trenchesin one of the rows-of gate trenchesare completely visible in, as are portions of the gate trenchesin two additional rows-,-.

4 FIG.B 192 160 192 190 192 181 180 192 192 180 182 As can also be seen in, a plurality of ohmic linesare defined in the upper surface of the semiconductor layer structure. The ohmic linesare the portions of the semiconductor layer structure that directly contact the source metallization. The ohmic linesare formed in the regions between adjacent rowsof gate trenches. A longitudinal axis of each ohmic lineextends in the y-direction and thus the longitudinal axes of the ohmic linesextend or “run” perpendicular to the longitudinal axes of the gate trenchesand the gate electrodes.

140 140 140 140 180 140 140 192 190 140 140 134 4 FIG.B The source regionmay be viewed as having first portionsA and second portionsB. The first portionsA are the portions that are in the regions between the gate trenches, as shown in. The second portionsB are the portions of the source regionthat are part of the ohmic line(i.e., the portions that contact the source metallization). In addition to the second portionsB of the source region, each ohmic line also includes a plurality of heavily-doped p-type well contact regions.

140 140 190 140 140 132 134 130 192 140 134 134 192 140 140 134 140 140 100 134 180 134 180 134 The second portionsB of the source regionprovide a current path for the on-state current to flow from the source metallizationinto the first portionsA of the source regionso that the on-state current may flow into the channel regions. The well contact regionsprovide a low resistance (e.g., ohmic) connection between the source metallization and the p-wells. In the depicted embodiment, each ohmic linecomprises alternating sections of source regionB and well contact regions. Embodiments of the present invention, however, are not limited thereto. For example, in other embodiments, the extent of the well contact regionsin the x-direction may be reduced so that each ohmic lineincludes a single continuous second portionB of the source regionthat has a plurality of well contact regionsformed therein that appear as “islands” in the second portionB of the source regionwhen the MOSFETis viewed from above. As another example, the well-contact regionsneed not be aligned with the gate trenchesas shown and/or the widths of the well-contact regionsin the y-direction can be varied to be less than or greater than the width of the gate trenches. The number of well contact regionsmay also be varied.

4 FIG.C 4 FIG.B 190 134 134 192 134 134 154 134 154 150 150 190 154 134 154 150 154 170 132 192 1 192 2 192 1 192 2 154 154 190 150 52 1 160 As can best be seen in, the source metallizationdirectly contacts the upper surface of the well contact region. The well contact regionextends the full length of the ohmic linein the x-direction. As such, the well contact regionforms the end walls of the gate trenches on either side of the well contact region. A p-type trench shield connection patternis formed underneath each p-type well contact region. Each trench shield connection patternmay directly contact one or more trench shielding regionsso as to electrically connect the trench shielding regionsto the source metallizationthrough the trench shield connection patternand the well contact region. As shown, the trench shield connection patternmay extend deeper into the semiconductor layer structure than the trench shielding regions. This may advantageously route currents during an avalanche breakdown event to flow primarily through the trench shield connection patterns, which may help protect the gate oxide layersthat are adjacent channel regionsof the device from increased electrical fields during an avalanche breakdown event. The dashed boxes-,-inthat illustrate the locations of the ohmic lines-,-also show the extend of the trench shield connection patterns. The trench shield connection patternsmay both provide an electrical connection between the source metallizationand the trench shielding regionsand may also act akin to the support shieldsincluded in power MOSFET′ as they will assist in lowering electric field levels in upper portions of the semiconductor layer structureduring reverse blocking operation.

4 4 FIGS.C andD 4 FIG.B 4 FIG.B 172 140 140 140 172 190 172 192 172 190 160 192 172 190 160 As can be seen in both, the intermetal dielectric layercovers the first portionsA of the source region, which are the portions of the source regionthat extend on top of the portions of the p-wells that include p-type channel regions. Thus, while not shown in(since dielectric layerand source metallizationare omitted in), the intermetal dielectric layerextends in stripes in the y-direction to completely cover the upper surface of the active region except for the ohmic lines, which are disposed in between the stripes of intermetal dielectric layer. The source metallizationis formed on the upper surface of the semiconductor layer structure(i.e., on the ohmic lines) and on the intermetal dielectric layers. The source metallizationmay comprise at least a source contact (e.g., a metal silicide layer) that forms ohmic contacts with the semiconductor layer structureand a bulk metallization layer on the source contact layer. Additional metal layers may be provided including, for example, one or more adhesion layers and/or one or more diffusion barrier layers.

4 FIG.D 130 180 132 102 104 106 100 130 182 132 132 104 106 190 140 132 120 110 106 100 130 192 132 182 As best shown in, the portions of each deep p-wellthat are adjacent a gate trenchact as channel regionsduring on-state operation. In particular, when appropriate bias voltages are applied to the gate, drain and source terminals,,of power MOSFET, a conductive n-type inversion layer is formed in the portion of each deep p-wellthat is adjacent a gate electrode(i.e., in the channel regions) will be inverted, allowing current to flow through the channel regions. Thus, a current path is created between the source and drain terminals,that flows through the source metallization, the source regions, the channel regions, the drift region, the substrateand the drain contact. The power MOSFETmay be turned off by changing the applied bias voltages (typically by lowering or removing the gate bias voltage). The portions of the p-wellsthat are underneath the ohmic lineswill not have channel regionsformed therein during on-state operation as they are not next to gate electrodes.

100 1 140 172 190 140 4 4 FIGS.A-D 1 1 FIGS.A-B 4 4 4 FIGS.A andC-D Power MOSFETofvaries in several significant aspects from power MOSFETof. First, shown in, the first portion of the source regionA is covered by a dielectric layerin the active region so that the source metallizationdoes not contact the first portion of the source regionA.

4 FIG.B 192 180 192 180 100 180 192 100 192 180 1 92 1 92 80 82 92 80 Second, as can best be seen in, the ohmic lineshave longitudinal axes that extend in a different direction than the longitudinal axes of the gate trenches, so that the longitudinal axes of the ohmic linescross the longitudinal axes of the gate trencheswhen the MOSFETis viewed from above. In the depicted embodiment, the longitudinal axes of the gate trenchescross the longitudinal axes of the ohmic linesat angles of 90° when the MOSFETis viewed from above. In other words, the ohmic linesextend perpendicularly to the gate trenches. Power MOSFETincludes ohmic lines, but in power MOSFETthe ohmic linesrun in parallel to the gate trenchesand the gate electrodes, with an ohmic lineprovided between each pair of adjacent gate trenches.

180 182 80 82 1 180 182 100 80 82 180 1 180 4 180 7 182 1 180 2 180 5 180 8 182 2 180 3 180 6 180 9 182 3 4 FIG.B Third, the gate trenchesand the gate electrodesare much shorter in the longitudinal direction than the corresponding gate trenchesand gate electrodesin power MOSFET. Because the gate trenchesand the gate electrodesare shorter, in power MOSFETmultiple gate trencheswith gate electrodestherein are aligned along common longitudinal axes. For example, as can be seen in, three gate trenches-,-,-with respective gate electrodestherein are aligned along a first longitudinal axis L, three additional gate trenches-,-,-with respective gate electrodestherein are aligned along a second longitudinal axis L, and three more gate trenches-,-,-with respective gate electrodestherein are aligned along a third longitudinal axis L.

4 FIG.B 1 34 82 100 134 134 192 182 100 Fourth, as can best be seen in, power MOSFETincludes p-type well contact regionsthat are positioned between each pair of adjacent gate electrodes. While power MOSFETincludes corresponding p-type well contact regions, the p-type well contact regionsare part of ohmic linesthat extend perpendicular to the gate electrodesin power MOSFET.

1 90 140 34 1 90 40 32 40 32 100 190 192 140 140 172 140 190 192 182 182 182 124 100 1 124 150 170 130 ohmic Fifth, in power MOSFET, the source metallizationdirectly contacts the entirety of the exposed upper surface of each source regionand each well contact region. In addition, in power MOSFET, the source metallizationdirectly contacts the portions of the source regionthat are above the channel regions, allowing the on-state currents to flow vertically through the source regionsinto the channels. In contrast, in power MOSFET, there may be significantly less direct contact between the source metallizationand the ohmic lines, and the upper surfaces of the first portionsA of the source regionare covered by dielectric layerso that they portionsA do not directly contact the source metallization. Since the ohmic linesare perpendicular to the gate electrodesand are not provided between adjacent gate electrodes, the distance between adjacent gate electrodesand hence the width of the JFET gapcan be reduced since the contact resistance is no longer a function of the width W. As discussed above, this reduction in cell pitch acts to reduce the on-state resistance of power MOSFETas compared to power MOSFET, since number of unit cells per unit area is increased. Moreover, the reduced width of the JFET gapsmay eliminate any need for support shields, since closely spaced trench shieldsprovide good shielding for the gate oxide layersand protect against punch-through the p-wellsduring reverse blocking operation.

100 160 190 192 192 190 192 120 192 140 140 182 192 192 4 4 FIGS.A-D 4 FIG.D In power MOSFET, the connections in the active region between the semiconductor layer structureand the source metallizationare formed along the ohmic lines. In the embodiment of, channels are not formed in any part of the ohmic lines. Thus, during on-state operation, current flowing in the source metallizationwill not flow vertically through the ohmic lineinto the drift region, but instead will flow in a horizontal direction out of the ohmic lineinto the first portionsA of the source regionthat are in between the gate electrodeson either side of the ohmic line. The direction of the current flow out of the ohmic linesis shown in.

4 4 FIGS.B andD 192 182 130 192 130 190 140 140 140 140 140 140 192 132 140 140 140 140 140 132 140 140 140 132 132 As can best be seen from, on-state current will not flow downwardly through the ohmic linebecause there is no gate electrodeadjacent the p-wellportion of the ohmic lineand hence this portion of the p-wellwill not invert during on-state operation. As such, the on-state current that flows from the source metallizationinto the portionsB of the source regionwill travel horizontally in the second portionsB of the source regionsB into the first portionsA of the source regionthat are on either side of the ohmic line. The channel regionsare underneath the first portionsA of the source region. As the on-state current flows into the first portionsA of the source region, some of the current will flow vertically through the source regionand the underlying channel region, while the remainder of the current will continue to flow horizontally through the first portionA of the source regionand only later turn to flow vertically through the source regionand the underlying channel region. The relative resistance of the current path determines how much and how far the current flows horizontally before turning to flow through the channel regions.

100 140 140 190 132 140 140 140 180 140 11 11 FIGS.A-D One unusual aspect of the design of power MOSFETis that the average length of the on-state current path is increased since the on-state current must flow horizontally through the second portionsB of the source regionto get from the source metallizationto the channel regions. Increasing the on-state current path is non-intuitive, as longer current paths generally have higher resistance. Here, however, the current path is increased by routing the current to flow horizontally through the source region, which is a highly-doped region that has a relatively low resistance. As such, the increase in the resistance caused by the increased current path may be less than the reduction in the resistance provided by the increased integration gained by the aggressive cell pitch. Moreover, as will be discussed below with reference to, in some embodiments, a silicide layer may be formed at the upper surface of the first portionsA of the source regions(i.e., the portions that are in between adjacent gate trenches). Since a silicide layer may have a resistance that is orders of magnitude less than the resistance of the source region, much of the horizontally-flowing on-state current will flow through the silicide regions, and thus the impact of the horizontally-flowing on-state current on the on-state resistance may be negligible.

Thus, the power MOSFETs according to embodiments of the present invention may have improved trade-offs between on-state resistance performance and device reliability.

100 In addition, power MOSFETmay also exhibit improved short circuit behavior. The “short circuit capability” of a power MOSFET refers to the time that the power MOSFET can operate at a specified temperature without damaging the device. Under so-called short circuit conditions the temperature of a power MOSFET may increase dramatically because of the large amount of power dissipated in the device when a high current passes through the device. The short circuit capability of a power MOSFET may be important because characteristics of the device and its packaging will determine the amount that the MOSFET heats up as a function of operating power. For example, if the power MOSFET conducts 500 amps at a voltage of 1200 volts, the power is 1200V*500 A=60 kilowatts. A power MOSFET with typical packaging may have a thermal impedance of, for example, 0.01° C./W. Thus, for such a MOSFET, operation at 60 kilowatts will heat the device up to about 600° C. (60 kilowatts*0.01° C./W=600° C.). Typically, a MOSFET may only sustain such temperatures without failing for a very short period of time such as, for example, 1 microsecond. In contrast, the same MOSFET might be able to operate at 200° C. for ten hours without failing.

In order to protect a MOSFET against such failure, a control circuit may be provided that senses when a short circuit condition is occurring and lowers the gate voltage (e.g., to 0 volts) in response thereto. The short circuit condition is not a normal operating condition and typically occurs because a larger system that includes the MOSFET is not operating as intended. The short circuit capability of a MOSFET is important, however, because when a short circuit condition occurs the control system must be able to shut off the gate voltage quickly to prevent failure of the device. The shorter the duration of the short circuit capability the faster the control circuit must be able to operate.

140 140 192 One way that the short circuit capability of a power MOSFET may be improved is by increasing the source resistance of the device, as the higher source resistance reduces the current during a short circuit event. Since the short circuit current will need to travel farther through the source regionduring a short circuit event (since the current must travel horizontally through portions of the source region), the source resistance is increased and the short circuit capabilities are therefore improved. The amount of improvement may be tuned, for example, by modifying the spacing between adjacent ohmic lines.

4 4 FIGS.A-D 4 FIG.B 100 160 120 182 160 1 182 160 2 192 1 160 1 1 2 1 100 Referring again to, pursuant to some embodiments of the present invention, power semiconductor devices such as power MOSFETare provided. These power semiconductor devices include a semiconductor layer structurethat comprises a drift regionhaving a first conductivity type (here, n-type), a first gate electrodeon the semiconductor layer structurethat extends along a first longitudinal axis L, a second gate electrodeon the semiconductor layer structurethat extends along a second longitudinal axis L, and a first ohmic line-that extends continuously in the semiconductor layer structurealong a first transverse axis T. The first and second longitudinal axes L, Lcross the first transverse axis Twhen the semiconductor deviceis viewed from above, as best shown in.

182 1 182 2 180 1 180 2 182 1 182 2 160 160 180 1 180 2 192 1 100 182 3 180 3 160 182 4 180 4 160 1 182 3 2 182 4 192 1 180 1 180 3 180 2 180 4 100 The first and second gate electrodes-,-are formed in respective gate trenches-,-. Consequently, the first and second gate electrodes-,-are both on the semiconductor layer structureand in the semiconductor layer structure. The first gate trench-and the second gate trench-each have a respective first end that is adjacent the first ohmic line-. The power semiconductor devicefurther comprises a third gate electrode-that extends along a longitudinal axis in a third gate trench-in the semiconductor layer structureand a fourth gate electrode-that extends along a longitudinal axis in a fourth gate trench-in the semiconductor layer structure, where the first longitudinal axis Lis colinear with the longitudinal axis of the third gate electrode-and the second longitudinal axis Lis colinear with the longitudinal axis of the fourth gate electrode-. The first ohmic line-is in between the first gate trench-and the third gate trench-and is also in between the second gate trench-and the fourth gate trench-when the semiconductor deviceis viewed from above.

1 2 1 1 2 100 172 1 182 1 182 2 160 182 1 182 2 The first longitudinal axis Lextends in parallel to the second longitudinal axis L, and the first transverse axis Tcrosses both the first longitudinal axis Land the second longitudinal axis Lat angles of 90°. The power semiconductor devicefurther includes a dielectric layerthat extends continuously in a direction parallel to the first transverse axis Tto cover the first gate electrode-and the second gate electrode-and an upper surface of the semiconductor layer structurethat is in between the first gate electrode-and the second gate electrode-.

4 FIG.B 100 192 1 160 2 1 2 2 100 1 2 182 1 182 2 192 1 192 2 100 As best shown in, the power semiconductor devicefurther comprises a second ohmic line-that extends continuously in the semiconductor layer structurealong a second transverse axis T, where the first and second longitudinal axes L, Lcross the second transverse axis Twhen the semiconductor deviceis viewed from above. The first transverse axis Textends in parallel to the second transverse axis T. The first gate electrode-and the second gate electrode-are positioned between the first ohmic line-and the second ohmic line-when the semiconductor deviceis viewed from above.

160 180 1 180 2 120 140 130 120 140 1 100 140 160 A first portion of the semiconductor layer structurethat is in between the first gate trench-and the second gate trench-comprises a drift regionhaving a first conductivity type (here, n-type), a source regionhaving the first conductivity type and a well regionhaving a second conductivity (here p-type) that is in between the drift regionand the source region. The first longitudinal axis Lextends in a first direction (the x-direction), and the semiconductor deviceis configured so that during on-state operation a source-drain current flows in the first direction (the x-direction, which is a horizontal direction) through the source regionin the first portion of the semiconductor layer structure.

4 FIG.A 1 160 180 1 180 2 2 180 1 1 2 While ina width Wof a portion of the semiconductor layer structurethat is in between the first gate trench-and the second gate trench-is shown to be slightly larger than a width Wof the first gate trench-, it will be appreciated that in other embodiments the width Wmay be less than the width W.

4 4 FIGS.A-D 100 160 120 140 130 120 140 100 182 1 160 1 182 2 160 2 172 160 172 182 1 182 2 140 140 180 1 180 2 172 140 140 Still referring to, pursuant to further embodiments of the present invention, power semiconductor devices such as power MOSFETare provided. These power semiconductor devices include a semiconductor layer structurethat comprises a drift regionhaving a first conductivity type (here, n-type), a source regionhaving the first conductivity type and a well regionhaving a second conductivity type (here, p-type) between the drift regionand the source region. The power MOSFETfurther comprises a first gate electrode-on the semiconductor layer structurethat has a first longitudinal axis Lthat extends in a first direction (the x-direction), a second gate electrode-on the semiconductor layer structurethat has a second longitudinal axis Lthat extends in the first direction (the x-direction), and a dielectric layerthat extends continuously on the semiconductor layer structurein a second direction (the y-direction), where the dielectric layercrosses the first gate electrode-, the second gate electrode-and a first portionA of the source regionthat is in between the first gate electrode-and the second gate electrode-. The dielectric layermay directly contact the first portionA of the source region.

4 4 FIGS.A-D 100 160 120 140 130 120 140 100 182 1 160 1 160 2 182 2 182 1 190 160 190 194 160 194 Continuing to refer to, pursuant to still further embodiments of the present invention, power semiconductor devices such as power MOSFETare provided. These power semiconductor devices include a semiconductor layer structurethat comprises a drift regionhaving a first conductivity type (here, n-type), a source regionhaving the first conductivity type and a well regionhaving a second conductivity type (here, p-type) between the drift regionand the source region. The power MOSFETfurther comprises a first gate electrode-on the semiconductor layer structurethat has a first longitudinal axis Lthat extends in a first direction (the x-direction), a second gate electrode on the semiconductor layer structurethat has a second longitudinal axis Lthat extends in the first direction, the second gate electrode-adjacent the first gate electrode-in a second direction (the y-direction) that is perpendicular to the first direction, and a source metallizationon an upper surface of the semiconductor layer structure, where the source metallizationhas a plurality of downwardly-extending protrusionsthat directly contact an upper surface of the semiconductor layer structure, where the downwardly-extending protrusionshave respective longitudinal axes that extend in the second direction.

4 4 FIGS.A-D 100 160 120 140 130 120 140 100 180 1 160 1 180 2 160 2 192 1 160 192 2 160 140 180 1 180 2 192 1 192 2 100 130 172 Continuing to refer to, it can be seen that power MOSFETcomprises a semiconductor layer structurethat comprises a drift regionhaving a first conductivity type (here, n-type), a source regionhaving the first conductivity type and a well regionhaving a second conductivity type (here, p-type) between the drift regionand the source region. The power MOSFETfurther comprises a first gate trench-in the semiconductor layer structurethat has a first longitudinal axis Lthat extends in a first direction (the x-direction), a second gate trench-in the semiconductor layer structurethat has a second longitudinal axis Lthat extends in the first direction, a first ohmic line-in the semiconductor layer structurethat has a third longitudinal axis that extends in a second direction (the y-direction), and a second ohmic line-in the semiconductor layer structurethat has a fourth longitudinal axis that extends in the second direction. A portion of the source regionthat is within a first region that is in between the first gate trench-, the second gate trench-, the first ohmic line-and the second ohmic line-when the semiconductor deviceis viewed in plan view completely covers a portion of the well regionthat is within the first region. A dielectric layercompletely covers an upper surface of the first region.

4 FIG.D 100 182 1 182 2 As shown in, the power MOSFETis configured so that during on-state operation a source-drain current flows in the first direction through a first portion of the source region that is in between the first gate electrode-and the second gate electrode-.

4 4 FIGS.A-B 5 12 FIGS.A-C 100 100 depict one example power MOSFETaccording to embodiments of the present invention. It will be appreciated that numerous modifications may be made thereto.illustrate various additional example embodiments of power MOSFETs according to embodiments of the present invention that are modified versions of power MOSFET.

5 5 FIGS.A-D 3 3 FIGS.A-B 5 5 FIGS.A-D 3 FIG.A 5 FIG.A 5 FIG.B 5 5 FIGS.C andD 5 FIG.B 5 FIG.B 200 200 100 200 200 200 200 200 260 5 5 5 5 illustrate a power MOSFETaccording to further embodiments of the present invention. At the device level, power MOSFETmay appear the same as power MOSFET, and henceaccurately depict power MOSFET.are various view of a small portion of power MOSFETthat corresponds to the box labelled A inthat illustrate the unit cell design of power MOSFET. In particular,is a schematic perspective view of the small portion of MOSFETandis a schematic top view of the small portion of power MOSFETwith the upper dielectric layers and the source metallization omitted to show the gate electrodes and the upper surface of the semiconductor layer structure.are cross-sectional views taken along linesC-C andD-D, respectively, ofwith the upper dielectric layers and the source metallization that are omitted inadded for context.

5 5 FIGS.A-D 4 4 FIGS.A-D 200 100 200 280 282 292 280 282 100 180 182 192 180 182 200 234 280 292 292 290 100 192 190 200 100 200 As can be seen by comparingto, power MOSFETprimarily differs from power MOSFETin that power MOSFEThas gate trenchesand gate electrodesthat extend continuously along respective longitudinal axes and discontinuous ohmic linesthat extend perpendicular to the gate trenches/gate electrodes,, whereas power MOSFEThas discontinuous gate trenchesand gate electrodesand continuous ohmic linesthat extend perpendicular to the gate trenches/gate electrodes,. Additionally, in power MOSFET, the well contact regionsare positioned adjacent sidewalls of the respective gate trenches, and the extent of the ohmic linesin the x-direction is increased to provide a similar contact area between the ohmic lineand the source metallizationthat is provided in power MOSFETbetween the ohmic linesand the source metallization. Otherwise, power MOSFETmay be identical to power MOSFET, and hence further description of power MOSFETwill be omitted here.

200 100 190 240 240 292 240 240 132 Power MOSFETwill operate in the same manner, discussed above, as power MOSFET, with the on-state current passing from the source metallizationto the second portionsB of the source regionthat are part of the ohmic lines, and then flowing horizontally through the first portionsA of the source regionsbefore turning to flow vertically through the channel regions.

6 6 FIGS.A-D 3 3 FIGS.A-B 6 6 FIGS.A-D 3 FIG.A 6 FIG.A 6 FIG.B 6 6 FIGS.C andD 6 FIG.B 300 300 100 380 180 300 300 300 300 6 6 6 6 illustrate a power MOSFETaccording to further embodiments of the present invention. Power MOSFETis similar to power MOSFET, but further includes a plurality of supplemental gate trenchesthat extend perpendicularly to the gate trenches.again accurately depict power MOSFET, andare views illustrating the small portion of power MOSFETthat corresponds to the box labelled A in. In particular,is a schematic perspective view of the small portion of MOSFETandis a schematic top view of the small portion of power MOSFETwith the upper dielectric layers and the source metallization are omitted.are cross-sectional views taken along linesC-C andD-D, respectively, ofwith the upper dielectric layers and the source metallization shown for context.

6 6 FIGS.A-D 4 4 FIGS.A-D 300 100 300 380 180 380 382 100 182 182 382 380 192 As can be seen by comparingto, power MOSFETdiffers from power MOSFETin that power MOSFETfurther includes a plurality of supplemental gate trenchesthat extend perpendicularly to the gate trenches. The provision of the supplemental gate trenchesalong with the supplemental gate electrodesformed therein converts the gate electrode structure of power MOSFETin which the gate electrodesonly extend in one direction (the x-direction) into a gate electrode mesh that has gate electrodes,that extend in two different directions. The provision of a gate electrode mesh may reduce the amount of gate runner that need be provided as the gate signal may be distributed through the gate electrode mesh. Each supplemental gate trenchmay run directly next to a respective one of the ohmic lines.

6 FIG.C 6 FIG.D 6 FIG.D 150 180 380 132 380 380 154 384 154 192 134 As can be seen in, the trench shielding regionis formed underneath both the gate trenchesand the supplemental gate trenches. As can be seen in, a channel regionis provided on the left side of each supplemental gate trench. In addition, a high energy p-type ion implantation is performed on the right side of each supplemental gate trench, as can be seen in, that forms a p-type trench shield connection patternto the right of each supplemental gate trench. A trench shield connection patternmay extend longitudinally underneath each ohmic lineand may be electrically connected to the source metallization through the well contact regions.

6 6 FIGS.A-D 300 160 120 182 160 1 182 160 2 192 1 160 1 382 380 160 382 2 1 2 182 1 382 182 2 382 2 382 1 160 120 140 130 120 140 150 180 1 180 2 380 160 154 380 Referring to, pursuant to further embodiments of the present invention, power semiconductor devices such as power MOSFETare provided that comprise a semiconductor layer structurethat comprises a drift regionhaving a first conductivity type (here, n-type), a first gate electrodeon the semiconductor layer structurethat extends along a first longitudinal axis L, a second gate electrodeon the semiconductor layer structurethat extends along a second longitudinal axis L, and a first ohmic line-that extends continuously in the semiconductor layer structurealong a first transverse axis T. Power MOSFET further comprises a supplemental gate electrodethat extends in a first supplemental gate trenchin the semiconductor layer structure, the supplemental gate electrodehaving a longitudinal axis Tthat is perpendicular to the first and second longitudinal axes L, L. A first end of the first gate electrode-contacts the supplemental gate electrodeand a first end of the second gate electrode-similarly contacts the supplemental gate electrode. The longitudinal axis Tof the supplemental gate electrodeextends in parallel to the first transverse axis T. The semiconductor layer structurecomprises a drift regionhaving a first conductivity type (here, n-type), a source regionhaving the first conductivity type, a well regionhaving a second conductivity (here, p-type) that is in between the drift regionand the source region, and a trench shielding regionhaving the second conductivity type that extends underneath the first gate trench-, the second gate trench-and the supplemental gate trench. The semiconductor layer structurefurther comprises a trench shield connection patternhaving the second conductivity type that extends along a sidewall of the supplemental gate trench.

300 100 300 154 300 380 154 300 100 Power MOSFETmay operate in the same fashion as power MOSFET, except that the gate signal is distributed throughout the gate mesh in power MOSFET. In addition, the trench shield connection patternin power MOSFETextends further in the x-direction (i.e., is wider), as it partly extends underneath the supplemental gate trench. The wider trench shield connection patternin power MOSFETmay provide improved electric field suppression during reverse blocking operation as compared to power MOSFET.

7 7 FIGS.A-B 7 FIG.A 7 FIG.B 7 FIG.A 400 300 400 7 7 illustrate a power MOSFETaccording to further embodiments of the present invention that is a slightly modified version of power MOSFET. In particular,is a schematic top view of a small portion of power MOSFETwith the upper dielectric layers and the source metallization omitted whileis a cross-sectional view taken along linesB-B ofwith the upper dielectric layers and the source metallization shown for context.

7 7 FIGS.A-B 6 6 FIGS.A-B 400 300 454 400 380 132 380 300 454 400 As can be seen by comparingto, power Mosfetdiffers from power MOSFETin that the trench shield connection patternin power MOSFETis formed on each side of each supplemental gate trench. This design decreases the total channel area (since the channel regionthat is provided on the left side of each supplemental gate trenchin power MOSFETis no longer present), but may have improved reverse blocking characteristics due to the expanded trench shield connection patternin power MOSFETwhich, as discussed above, also acts as a support shield.

8 8 FIGS.A-B 8 FIG.A 8 FIG.B 8 FIG.A 500 300 500 8 8 illustrate a power MOSFETaccording to further embodiments of the present invention that is a slightly modified version of power MOSFET. In particular,is a schematic top view of a small portion of power MOSFETwith the upper dielectric layers and the source metallization omitted whileis a cross-sectional view taken along linesB-B ofwith the upper dielectric layers and the source metallization shown for context.

8 FIG.A 6 8 FIGS.B andA 500 154 552 154 380 552 380 552 500 500 300 552 380 380 552 500 As shown in, power MOSFETincludes both trench shield connection patternsas well as separate support shields. The trench shield connection patternsare provided on a first side of the supplemental gate trenchesand the support shieldsare provided on the other side of the supplemental gate trenches. As can best be seen by comparing, each second support shieldeliminates some of the channel area in power MOSFETso that power MOSFEThas less channel area than power MOSFET. However, each second support shieldis spaced apart from its associated supplemental gate trenchso that some of eliminated channel area is regained by forming spaced apart channel regions along one side of each supplemental gate trench. The provision of the second support shieldsmay improve the reverse blocking performance of power MOSFET.

9 FIG. 6 FIG.A 9 FIG. 600 300 is a schematic top view of a power MOSFETthat is yet another modified version of the power MOSFETof. Once again, inthe upper dielectric layers and the source metallization are omitted to show the gate electrodes and the upper surface of the semiconductor layer structure.

6 9 FIGS.B and 9 FIG. 600 300 380 192 192 380 As can be seen by comparing, power MOSFETdiffers from power MOSFETin that the supplemental gate trenchesare spaced apart from the ohmic lines. The embodiment ofillustrates that the number and positioning of the ohmic linesmay be selected independently of the number and positioning of the supplemental gate trenches.

10 FIG. 4 4 FIGS.A-D 10 FIG. 4 FIG.B 10 FIG. 700 100 762 160 is a schematic top view of a power MOSFETthat is a modified version of the power MOSFETof. The view ofcorresponds to the view of, except that ina silicide layeris shown that is formed on the upper surface of the semiconductor layer structure.

10 FIG. 10 FIG. 4 4 4 FIGS.A andC-D 10 FIG. 10 FIG. 700 100 700 762 762 140 140 140 140 192 172 762 762 140 140 762 172 172 762 As shown in, power MOSFETmay be identical to power MOSFET, except that power MOSFETfurther includes the silicide layer. The silicide layermay be formed to cover the entirety of the first portionA of the source region. As discussed above, the first portionA of the source regionis the port that is not part of the ohmic lines. While not shown in, the dielectric layermay completely cover the silicide layerso that the lower surface of the silicide layerdirectly contacts the upper surface of the first portionsA of the source regionwhile the upper surface of the silicide layerdirectly contacts the intermetal dielectric layer. In other words, the dielectric layerofis also provided in, although it is not shown inin order to show the silicide layer.

4 FIG.D 140 140 132 172 140 140 140 140 140 130 140 140 132 762 762 140 762 140 As described above with reference to, some of the on-state current travels horizontally through the first portionsA of the source regionbefore the on-state current transitions to flow vertically through the channel regions. This horizontal current flow occurs because the dielectric layercovers the first portionsA of the source regionso that current can only flow throughout the first portionsA of the source regionthrough such horizontal current flow. The current flows horizontally because the resistance of the source regionis much lower than the resistance of the p-wells, and hence the current will tend to spread through the first portionsA of the source regionbefore flowing downwardly through the channel regions. As noted above, this horizontal current flow increases the length of the on-state current path, and the increased path length increases the on-state resistance. By providing the silicide layer, much of the horizontal current flow will occur in the silicide layerrather than in the source region. As the silicide layerhas a very low resistance (orders of magnitude lower than the source region), the increase in on-state resistance caused by the increased length of the current path can be made de minimis.

192 190 192 762 172 700 10 FIG. It should be noted that a silicide layer (not shown) will typically also be formed that covers the ohmic lineswhen the source metallizationis formed to contact the ohmic lines. This silicide layer is not depicted into highlight the silicide layerthat is formed underneath the dielectric layerto facilitate low-resistance horizontal current flow in power MOSFET.

4 4 4 10 FIGS.A,C-D and 700 160 140 762 140 172 762 762 140 172 Thus, referring to refer to, pursuant to still further embodiments of the present invention, power semiconductor devices such as power MOSFETare provided. These power semiconductor devices include a semiconductor layer structurethat comprises a source regionhaving a first conductivity type (here, n-type). A silicide layeris formed on the source region, and a dielectric layeris formed on the silicide layerso that the silicide layerdirectly contacts both the source regionand the dielectric layer.

11 11 FIGS.A-C 11 FIG.A 11 FIG.B 11 FIG.A 11 FIG.C 11 FIG.A 800 800 800 11 11 The above-discussed embodiments of the present invention are all vertical power MOSFETs having trench gates. It will be appreciated, however, that embodiments of the present invention are not limited thereto. For example,illustrate a vertical power MOSFETaccording to further embodiments of the present invention that has a planar gate design. In particular,is a schematic top view of a small portion of power MOSFETwith the upper metallization and dielectric layers omitted, whileis a schematic perspective view of the portion of power MOSFETin the region B ofwith the upper metallization and dielectric layers added for context.is a cross-sectional view taken along lineC-C ofwith the upper metallization and dielectric layers added for context

11 11 FIGS.A-C 4 4 FIGS.A-D 800 100 100 182 180 160 800 882 860 860 As can be seen by comparingto, power MOSFETis very similar to power MOSFET, with the primary difference being that power MOSFEThas gate electrodesthat are formed in gate trencheswithin the semiconductor layer structurewhile power MOSFEThas gate electrodesthat are formed on the uppermost surface of the semiconductor layer structure(with a gate oxide layer insulating the gate electrodes from the semiconductor layer structure).

In the description above, each example embodiment has a certain conductivity type. It will be appreciated that opposite conductivity type devices may be formed by simply reversing the conductivity of the n-type and p-type layers in each of the above embodiments. Thus, it will be appreciated that the present invention covers both n-channel and p-channel devices for each different device structure (e.g., MOSFET, IGBT, etc.).

The present invention has primarily been discussed above with respect to silicon carbide based power semiconductor devices. It will be appreciated, however, that silicon carbide is used herein as an example and that the devices discussed herein may be formed in any appropriate wide band-gap semiconductor material system. As an example, gallium nitride based semiconductor materials (e.g., gallium nitride, aluminum gallium nitride, etc.) may be used instead of silicon carbide in any of the embodiments described above.

References are made herein to a first element extending deeper into a semiconductor layer structure of a gate trench semiconductor device than a second element. The depth that an element extends into a semiconductor layer structure refers to a distance that the element extends from an upper surface of the semiconductor layer structure, where the upper surface is the surface from which the gate trenches extend into the semiconductor layer structure. Thus, if a first element extends deeper into a semiconductor layer structure than a second element, this means that a lowermost surface of the first element is farther from the upper surface of the semiconductor layer structure than is a lowermost surface of the second element. In the embodiments discussed above, the depth is the distance in the z-direction from the uppermost surface of the semiconductor layer structure.

Embodiments of the present invention have been described above with reference to the accompanying drawings, in which embodiments of the invention are shown. It will be appreciated, however, that this invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth above. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Herein, the term “plurality” means two or more. Herein, “substantially” means within +/−10% unless otherwise indicated.

As used herein, two elements of a semiconductor device are considered to “vertically overlap” if an axis that is perpendicular to the major surfaces of a semiconductor layer structure of the semiconductor device intersects both elements.

It will be understood that, although the terms first, second, etc. are used throughout this specification to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. The term “and/or” includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “top” or “bottom” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

Embodiments of the invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. The thickness of layers and regions in the drawings may be exaggerated for clarity. Additionally, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Embodiments of the invention are also described with reference to a flow chart. It will be appreciated that the steps shown in the flow chart need not be performed in the order shown.

Some embodiments of the invention are described with reference to semiconductor layers and/or regions which are characterized as having a conductivity type such as n-type or p-type, which refers to the majority carrier concentration in the layer and/or region. Thus, n-type material has a majority equilibrium concentration of negatively charged electrons, while p-type material has a majority equilibrium concentration of positively charged holes. Some material may be designated with a “+” or “−” (as in n+, n−, p+, p−, n++, n−−, p++, p−−, or the like), to indicate a relatively larger (“+”) or smaller (“−”) concentration of majority carriers compared to another layer or region. However, such notation does not imply the existence of a particular concentration of majority or minority carriers in a layer or region.

In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.